Listen to this article

Microsoft struck an alliance with one of the leading open-source software companies on Thursday, signalling what could come to be seen as a landmark agreement in the war that has divided the software world in recent years.

As part of the deal Microsoft said it would for the first time put some of its marketing effort behind a version of the Linux operating system.

Microsoft has gradually revised its opposition to Linux, reflecting the fact that the rival system has become a mainstream part of many companies’ technology systems and that customers have started to demand easier ways to link systems that run on the rival software products.

Steve Ballmer, Microsoft’s chief executive, who once called Linux “a cancer that attaches itself in an intellectual property sense to everything it touches”, yesterday said: “I certainly realise Linux plays an important role in the infrastructure of our customers and will continue to play an important role.”

Microsoft said it would co-operate with Novell, whose Suse Linux is one of the most widely used versions of the software, to make the rival technologies work better together. The companies said they had been pressed by customers who use both technologies to overcome technical, business and legal disagreements that have made it difficult to run their systems alongside each other.

The agreement was designed to give users “technical interoperability and patent peace of mind,” said Mr Ballmer.

In what it claimed was a legal breakthrough, Microsoft said it had created an “intellectual property bridge” between open-source and proprietary software. It said it would not enforce any patent rights against users of Suse Linux over any of Microsoft’s IP that is included in the software, and that in return it will receive payments from Novell to reflect the concession.

It also said it would offer marketing support to the Novell product, though Mr Ballmer said the agreement did not reflect any change to Microsoft’s strong belief about the superiority of its own operating system.

The two also said they would collaborate technically to make it easier for companies to run Suse Linux and Windows machines alongside each other. That capability has become increasingly important as companies try to “virtualise” data centres in a way that lets them shift tasks more easily between different machines to even out their computing workload.

Linux has grown to become a strong alternative to Windows in the server business. In the third quarter of this year $1.5bn of new servers were sold with the Linux operating system installed, against against $4.2bn of servers that carried Windows, according to research firm IDC.